In recent years, optical disk drives have rapidly became standard-equipment on personal computers, and they have become an indispensable feature of personal computers along with hard disk drives. While CD-ROM drives have initially made up the majority of optical disk drives, DVD-ROM drives having a larger capacity than that of CD-ROM drives or recordable or rewritable CD-R/CD-RW drives which are standard-equipment on personal computers these days, and further, DVD-R or DVD-RAM drives have appeared on the market. Thus, there are no bounds to enhancement in performance and function of optical disk drives.
An example of an optical disk drive is illustrated in FIG. 1. In the figure, numeral 11 denotes an optical disk (hereinafter, merely referred to as a disk), numeral 12 denotes a spindle motor for rotating the disk 11, numeral 13 denotes a pickup for reading data on the disk 11, numeral 14 denotes a lens which focuses a reflected light beam from the disk 11 onto the pickup 13, numeral 15 denotes a feed which movably supports the pickup 13, numeral 16 denotes a feed motor which drives the feed 15 to move the pickup 13, numeral 17 denotes a driver IC which performs control for driving the spindle motor 12, the pickup 13, the feed motor 16, and a digital signal processor IC 19, numeral 18 denotes an analog front end IC which processes an RF signal from the pickup 13, numeral 19 denotes a digital signal processor IC which processes a digital signal from the analog front end IC 18, numeral 20 denotes a decoder IC for decoding the digital signal outputted from the digital signal processor IC 19, numeral 21 denotes a CPU which controls the driver IC 17, the analog front end IC 18, the digital signal processor IC 19, and the decoder IC 20 of the optical disk drive, and numeral 22 denotes a host, such as a personal computer body or the like, which issues an instruction to the optical disk drive.
Next, the operation will be described. The disk 11 is rotationally driven at a constant linear velocity or a constant angular velocity by the spindle motor 12. To the rotating disk 11, the pickup 13 moves from the inner circumference toward the outer circumference of the disk in a radial direction, and applies a laser beam onto the disk surface to read data thereon from a change of its reflected light. Data called pits, which are generally referred to as tracks, are spirally recorded on the disk surface, and in order to read the data accurately, the pickup 13 drives the lens 14, which is supported by a wire in a housing in the pickup 13, vertically to the disk surface, and focuses the laser beam onto the disk surface. Further, the pickup 13 detects a deviation of the laser beam from the center of the track by detecting a change of the reflected laser beam from the disk surface, and drives the lens 14 horizontally to the disk surface in a radial direction to perform tracking control so that the laser beam is positioned in the center of the data (track). The lens 14 is subjected to focus servo control and tracking servo control with the disk 11, and the pickup 13 reads the data from the disk surface and sends them to the analog front end IC 18. Thereafter, the reproduced data are transferred to the host 22 via the digital signal processor IC 19 and the decoder IC 20.
Since data are spirally recorded on the disk surface as described above, the pickup 13 has to move from the inner circumference toward the outer circumference with the passage of time. There are two methods of moving the pickup 13, one is a method of moving the lens 14 in the housing of the pickup 13 and the other is a method of moving the feed 15 to which the pickup 13 is fixed.
There is generally employed a method of initially moving the lens 14 to follow the track, and then moving the feed 15 to return the lens 14 to the center of the housing when the lens 14 is moved by a predetermined distance or more from the center of the housing. Meanwhile, when data at an arbitrary position on the disk surface are read according to an instruction from the exterior (such as the host), a seek operation is performed. The seek operation is fast-forward or fast-rewind, in which the number of tracks from the present position to a target position is obtained by calculation, and the pickup 13 is moved by the number of tracks at high speed.
There are two methods of moving the pickup 13 in the seek operation. A seek which moves the feed 15 to carry the pickup 13 to a target position is generally referred to as a feed seek, which is employed for a move of a relatively long distance. On the other hand, a seek which does not move the feed 15, but moves the lens 14 in the housing of the pickup 13 so that the lens 14 reaches a target position, is generally referred to as a kick seek, which is employed for a move of a relatively short distance. The seek operation is performed by combining these two kinds of seeks.
Since, as shown in FIG. 2, a lens 24 is supported by wires 25 and 26 in a pickup 23 in the above-described optical disk drive, it is extremely vulnerable to external vibrations or the like. That is, since the above-described feed seek is, so to speak, an external vibration for the pickup, too fierce an acceleration or deceleration of the feed movement makes a lens 34 deviate from the center in a pickup 33 when the feed seek is ended, as shown in FIGS. 3(a) and 3(b). FIG. 3(a) illustrates a case where the lens 34 is shifted toward the outer circumference in the pickup 33 due to a seek toward the inner circumference, and FIG. 3(b) illustrates a case where the lens 34 is shifted toward the inner circumference in the pickup 33 due to a seek toward the outer circumference.
Another problem is that the feed inertially continues moving even after the feed seek is ended, resulting in an offset of the lens. FIGS. 4(a) and 4(b) illustrate a positional alteration of the lens in the pickup after the feed seek. FIG. 4(a) shows the state when the feed seek has just ended. At this point in time, the lens 44 is located in the center of the pickup 43. However, actually, the feed continues moving inertially, and the lens 44 may shift by the time of the kick seek as shown in FIG. 4(b). This results in the same problem as the above-described offset of the lens due to too fierce acceleration or deceleration of the feed movement.
Next, what kind of adverse effect the offset of the lens has on the servo control will be described with reference to FIG. 5. Usually, the lens is located at a lens position 52, that is, the center of the pickup, and refracts a light from a laser 54 to focus it onto the surface of a disk 51. The lens has a function of returning a reflected light from the disk 51 to a photoreceptor unit 55 of the pickup. However, when the lens is shifted and located at a lens position 53, the reflected light from the laser 54 is not incident on the photoreceptor unit 55 as shown by a dotted line. Therefore, accurate data reading is disturbed, and further, the tracking servo becomes unstable when the lens is shifted because the tracking servo generates a positional signal from the reflected light of the disk.
When an instruction of read from an arbitrary position is issued by the host 22 shown in FIG. 1, it is ideal that a seek position 63 is set just before a read start position (target position) 62 as the arbitrary position as shown in FIG. 6. The distance between the seek position 63 and the read start position 62 is shorter than the distance of one sector 61. Actually, however, a lens offset may occur by the seek, as described above, and therefore, a seek position 73 is set several sectors 77 before a read start position 72 (at the inner circumference of the disk), and play tracing is made to the read start position 72 at the same tracing speed as a speed of normal playback to reduce a lens offset 74 from a lens offset 75 at seek end to a lens offset 76 at read start, as shown in FIG. 7.
However, the situation where the seek position is several sectors 77 before the read start position 72 is the same in any seek, and thus, additional access time is required for the time of play tracing for the several sectors 77. Further, even when the seek position is set as described above, if the amount of generated lens offset is extremely large, the lens offset is not removed by the time of read start, and a read error may occur.
The present invention is made to solve the above-mentioned problems and has for its object to provide a controller for driving a pickup of an optical disk drive, which can perform a read after stabilizing movement of a lens.